New immediate edit/loop-range settings from current clip extents, accessible on the main menu (Clip/Range Set, Loop Set) and from MIDI clip editor menu as well (File/Range Set, Loop Set).

might be just what you're asking ;)

re. my commands ("h" to get back to the start mark, and ";" to get forward to it) do not work in midi clip edit mode..?
that's probably correct: keyboard shortcut configuration settings are kept separate and independent between main application window and all midi clip editor windows. there are some which are equivalent in function like transport-backward and -forward. for those cases you'll have to repeat the shortcut setting on the midi clip editor window too (Help/Shortcuts...) , otherwise it will keep the factory defaults eg. backspace for transport-backward.